1. Field of the Invention
This invention relates to a valve plug threadedly engaged with a member such as a valve stem so as to be inserted from an open end of the member into a passage defined inside the member for charging with and/or releasing from a compressed fluid, thereby to close an inner smaller diameter portion of the passage. The invention further relates to a valve provided with the valve plug.
2. Description of the Related Art
U.S. Pat. No. 6,266,971 to Schroder et al. discloses one of conventional valves of the above-described type. The disclosed valve comprises a valve plug including a threadedly engaging member with a tapered portion formed integrally with a distal end thereof. The valve plug is threadedly engaged with a cylindrical stem so as to be inserted into a passage defined in the stem, so that the tapered portion of the valve plug is inserted into a smaller diameter portion of the passage defined in an inner part of the passage, thereby closing the passage. The valve plug has a tool cavity formed in an end face opposite the tapered portion and a communication hole extending from an inner face of the tool cavity to a side face of the plug near the tapered portion. When the tapered portion is departed from the smaller diameter portion, a compressed fluid is allowed to pass via the communication hole through the valve plug.
In the above-noted valve plug, until the valve plug is further threadedly engaged with the stem after abutment of the tapered portion against the smaller diameter portion so that the tapered portion adheres closely to the smaller diameter portion, the tapered portion is slidingly turned while being pressed against the smaller diameter portion.
As a result, sliding portions of the tapered portion and the valve plug are worn out, whereupon the valve plug has a low reliability in its repeated use. Furthermore, the communication hole is closed while a tool is in engagement with the tool cavity. Consequently, releasing from the compressed fluid via the smaller diameter portion cannot be carried out while the valve plug is threadedly engaged with the tool.